The loss-of-function PCSK9Q152H variant increases ER chaperones GRP78 and GRP94 and protects against liver injury
Paul F. Lebeau, Hanny Wassef, Jae Hyun Byun, Khrystyna Platko, Brandon Ason, Simon Jackson, Joshua Dobroff, Susan Shetterly, William G. Richards, Ali A. Al-Hashimi, Kevin Doyoon Won, Majambu Mbikay, Annik Prat, An Tang, Guillaume Paré, Renata Pasqualini, Nabil G. Seidah, Wadih Arap, Michel Chrétien, Richard C. Austin
Paul F. Lebeau, Hanny Wassef, Jae Hyun Byun, Khrystyna Platko, Brandon Ason, Simon Jackson, Joshua Dobroff, Susan Shetterly, William G. Richards, Ali A. Al-Hashimi, Kevin Doyoon Won, Majambu Mbikay, Annik Prat, An Tang, Guillaume Paré, Renata Pasqualini, Nabil G. Seidah, Wadih Arap, Michel Chrétien, Richard C. Austin
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Research Article Hepatology Vascular biology

The loss-of-function PCSK9Q152H variant increases ER chaperones GRP78 and GRP94 and protects against liver injury

Abstract

Individuals harboring the loss-of-function (LOF) proprotein convertase subtilisin/kexin type 9 Gln152His variation (PCSK9Q152H) have low circulating low-density lipoprotein cholesterol levels and are therefore protected against cardiovascular disease (CVD). This uncleavable form of proPCSK9, however, is retained in the endoplasmic reticulum (ER) of liver hepatocytes, where it would be expected to contribute to ER storage disease (ERSD), a heritable condition known to cause systemic ER stress and liver injury. Here, we examined liver function in members of several French-Canadian families known to carry the PCSK9Q152H variation. We report that PCSK9Q152H carriers exhibited marked hypocholesterolemia and normal liver function despite their lifelong state of ER PCSK9 retention. Mechanistically, hepatic overexpression of PCSK9Q152H using adeno-associated viruses in male mice greatly increased the stability of key ER stress-response chaperones in liver hepatocytes and unexpectedly protected against ER stress and liver injury rather than inducing them. Our findings show that ER retention of PCSK9 not only reduced CVD risk in patients but may also protect against ERSD and other ER stress–driven conditions of the liver. In summary, we have uncovered a cochaperone function for PCSK9Q152H that explains its hepatoprotective effects and generated a translational mouse model for further mechanistic insights into this clinically relevant LOF PCSK9 variant.

Authors

Paul F. Lebeau, Hanny Wassef, Jae Hyun Byun, Khrystyna Platko, Brandon Ason, Simon Jackson, Joshua Dobroff, Susan Shetterly, William G. Richards, Ali A. Al-Hashimi, Kevin Doyoon Won, Majambu Mbikay, Annik Prat, An Tang, Guillaume Paré, Renata Pasqualini, Nabil G. Seidah, Wadih Arap, Michel Chrétien, Richard C. Austin

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Figure 4

ER retention of PCSK9 increases the stability of UPR chaperones GRP78 and GRP94.

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ER retention of PCSK9 increases the stability of UPR chaperones GRP78 an...
(A) The livers of Pcsk9–/– mice (n = 5) treated with AAV encoding EV, hPCSK9 WT, and ER-retained variant hPCSK9Q152H or hLDLRG544V were examined for expression of ER-resident chaperones GRP78 and GRP94 by IHC staining. (B) Relative staining intensities were quantified using ImageJ software. (C and D) GRP78 and GRP94 protein and mRNA levels were also assessed using immunoblots and real-time PCR. (E and F) Pcsk9–/– mice and age-matched Pcsk9+/+ controls (n = 5) were fed either normal chow diet (NCD) or high-fat diet (HFD) for 12 weeks and examined for GRP78 and GRP94 expression by IHC staining and immunoblots. Values are represented as mean ± SD. ANOVA was used for all statistical comparisons (A–F). *P < 0.05. Scale bars: A and E, 200 μm.